: The identification and characterization of proteins is an essential part of understanding biological processes. With the recently sequenced human genome, as well as the genomes of model organisms and pathogens, the next great challenge is to understand how the proteins encoded in these genomes function in their normal activities and in those that cause disease. Joining this challenge, a large number of research projects at Emory University focus on the identification of proteins, the characterization of protein posttranslational modifications, and the study of protein-ligand interactions. Because a significant portion of this work requires specialized instrumentation , much of this work is carried out by the Emory University Microchemical Facility (EMF). This core facility provides protein sequencing services by Edman degradation and triple quadrupole tandem mass spectrometry (triple quadrupole). While this technology is powerful and accurate, it is limited in two critical ways. The first is that sufficient sample material must be provided to determine the sequence of the peptides generated from purified proteins. This restricts analyses to abundant proteins or proteins that have specific reagents that allow their purification from complex sources. Second, the current instrumentation has limitations with regard to fully characterizing post-translational modifications. Elucidating such modifications is important to understand biological signal cascades and protein function. To improve the capabilites of the EMF and to aid the research efforts of Emory Investigators, we request funds to purchase a Q-TOF mass spectrometer. The instrument requires an order of magnitude less starting material for sequence determination than our triple quadrupole MS. The instrument will be on line with a nano-capillary HPLC, allowing mass and/or sequence determinations from a series of proteolytic digestions. This will increase greatly the success, speed, and characterization of samples. The instrument will also be used to analyze the nature of posttranslational modifications, such as determining the nature of phosphorylation and glycosylation of investigator?s samples. This state-of-the-art instrument?s flexibility, sensitivity, and accuracy will increase greatly the productivity of the research projects described as well as other NIH projects at Emory.